The present invention relates to standardized mechanical interface (SMIF) systems for reducing particle contamination and more particularly to transportable containers apparatus which are hermetically sealable.
A standardized mechanical interface (SMIF) has been proposed by the Hewlett-Packard Company as disclosed in U.S. Pat. Nos. 4,532,970 and 4,534,389. The purpose of the SMIF system is to reduce particle fluxes onto wafers. This end is accomplished by mechanically ensuring that during transportation, storage and processing of the wafers, the gaseous media (such as air or nitrogen) surrounding the wafers is essentially stationary relative to the wafers and by ensuring that particles from the ambient environment do not enter the immediate wafer environment.
The SMIF system above consists of two parts: (1) a controlled environment including a clean process equipment canopy surrounding the wafer-handling mechanism of each processing machine, and (2) a small, clean box having a quiet internal environment for carrying wafers from processing machine to processing machine.
Systems of the above type are concerned with particle sizes which range from below 0.1 micrometers to above 200 micrometers. Particles with these sizes can be very damaging in semiconductor processing because of the small geometries employed in fabricating semiconductor devices. Typical semiconductor processes today employ geometries which are 1 micrometer and under. Unwanted contamination particles which have geometries measuring greater than 0.1 micrometer substantially interfere with 1 micrometer geometry semiconductor devices. The trend, of course, is to have smaller and smaller semiconductor processing geometries which today in research and development labs approach 0.1 micrometer and below. In the furture, geometries will become smaller and smaller and hence smaller and smaller contamination particles become of interest.
In typical processing environments today, "clean rooms" are established in which through filtering and other techniques, attempts are made to remove particles having geometries greater than 0.03 micrometers and above. There is a need, however, to improve the processing environment. In a clean room, wafers and other semiconductor processing articles are exposed to the full clean room environment. Since different people, different types of equipment and materials are also present in the clean room environment, the clean room cannot be maintained as particle free as desired. It is virtually impossible to maintain clean rooms free of particles of a 0.1 micrometer size and below.
For this reason, systems such as the SMIF system have come under consideration. The proposed SMIF system, however, has some deficiencies. When SMIF boxes become contaminated, it is very difficult to remove small contaminant particles since the force of attraction of small particles to surfaces of the equipment is very high. When small particles become attached to a surface such as a SMIF box, they are not effectively removed by filtration techniques. Circulating and filtering air or other gas within a box does not readily remove the contamination particles which are attracted and held in contact with surfaces. However, whenever an object such as a SMIF box is disturbed, by bumping for example, many small particles are freed from the surface and find their way as contaminants onto any semiconductor or other article which is present in the box. While scrubbing and washing techniques have been developed for removing small particles from equipment and surfaces, these processes tend to be cumbersome and furthermore are not entirely effective.
There have since been sealable transportable containers such as one described in U.S. Pat. No. 4,434,891, which discloses a container for a magnetic disc pad eye. That container included a top portion having a screw and therefore requiring manual means to remove the contents from the box interior space.
Previous SMIF concepts have included the principle that the wafers move from the transportable container to the processing equipment through various apparatus by disturbing the least amount of air within the processing equipment. Thus the still air concept has prevaded prior SMIF transportable containers. The advantage of this is that any particulates in the air would not damage semiconductor wafers because the air remained relatively still during the transferring process. While this principle is still valid, it has been found that stagnant air too, has many particles which may also cause damage simply by static attraction. The recognition that stagnant air causes contamination and damage has created a need for active localized filtering of the SMIF box and the environments with which the semiconductor articles are exposed. This recognition is a departure from the previous SMIF concept which employed no active filtering means. The need for active filtering at localized areas and under specific conditions and at desired times has been left to this invention.
In accordance with the above background, there is a need for an improved system which can be standardized and which is effective for reducing contamination using an active filtering system.